Bishop came down hard on diocese with casual attitude? (8)
I believe the answer is:
blithely
'with casual attitude?' is the definition.
'bishop came down hard on diocese' is the wordplay.
'bishop' becomes 'b' (abbreviation used in chess).
'came down' becomes 'lit' (old-fashioned term for descended).
'hard' becomes 'h'.
'on' means one lot of letters go next to another.
'diocese' becomes 'ely' (I've seen this before).
'b'+'lit'+'h'+'ely'='BLITHELY'
(Other definitions for blithely that I've seen before include "in careless way" , "Merrily" .)